Hypernuclear weak decay experiments at KEK; nucleon inclusive measurement

摘要

Recent high quality neutron spectrum of C-12(Lambda) made it possible to derive the Gamma(n)/Gamma(p) ratio directly comparing its yield to that of the previous proton spectrum. The derived ratio, (0.45-0.51) +/- 0.15, was significantly smaller than unity showing the dominance of the proton induced NMWD channel for the first time and agreed well with the recent theoretical calculations. However, this ratio still has inherent ambiguity due to the two nucleon induced NMWD and the nuclear final state interaction (FSI). Recently exclusive coincidence measurements of each NMWD channel of He-5(Lambda) and C-12(Lambda) were made in order to reduce such ambiguities and confirmed the proton channel dominance in both inclusive and exclusive data. Important progress also has been made in the measurement of the decay asymmetry parameter, alpha(p)(NM), of the NMWD of He-5(Lambda) and C-12(Lambda) with much improved statistics over previous experiments. We have obtained small alpha(p)(NM) values for both 5 He and C-12(Lambda), close to zero within one a sigma level. The nearly identical alpha(p)(NM) values of He-5(Lambda) and C-12(Lambda) indicates that the NMWD mechanisms of s- and p-shell hypernuclei are similar. However, the theoretical results for alpha(p)(NM) the range of -0.6-(-0.7).